PInvoke

Platform Invocation Services (PInvoke) is a .NET runtime feature that enables managed code to call functions exported by unmanaged libraries, such as native Windows API DLLs or cross‑platform shared libraries. It is used to reuse native code or access operating system facilities from managed code.

PInvoke declares a managed method as external and annotates it with DllImport, specifying the library name and optional entry point. The runtime marshals data between managed and unmanaged representations and applies the chosen calling convention. Strings, arrays, structs, and handles often require explicit marshaling rules via attributes such as MarshalAs and StructLayout.

Example: static class NativeMethods { [DllImport("user32.dll", CharSet = CharSet.Unicode, SetLastError = true)] public static extern int MessageBox(IntPtr hWnd, string text, string caption, uint type); }

Platform differences affect behavior. Windows typically uses .dll libraries; Linux uses .so and macOS uses .dylib. Cross‑platform code may need per‑platform signatures or dynamic loading with NativeLibrary.Load. It is important to specify appropriate character sets, calling conventions, and platform ABI to ensure correct operation.

Limitations and best practices include minimizing marshaling in hot paths, preferring simple data types, and using SafeHandle for native resources to ensure deterministic release. Signature or calling convention mismatches can crash a process. Use SetLastError and GetLastWin32Error semantics when interoperating with APIs that report errors. Consider wrapping native calls in a managed abstraction to reduce risk and improve maintainability.